1. Field of the Invention
The present invention relates to an eye fundus examination apparatus for examining an eye fundus in an ophthalmic hospital, e.g., an eye blood flowmeter such as an eye fundus blood flowmeter for measuring a blood flow velocity and rate by illuminating an eye to be examined with a laser beam, receiving scattered reflected light, and analyzing it. In addition, the present invention relates to a method of displaying an eye fundus image and measurement data at the time of measurement of a blood flow velocity and rate.
2. Related Background Art
As a conventional eye blood flowmeter, a laser Doppler eye fundus blood flowmeter which tracks an eye fundus blood vessel of an eye to be examined and measures the absolute blood flow velocity in the tracked blood vessel is known. As such a laser Doppler eye fundus blood flowmeter, for example, the apparatus disclosed in Japanese Patent Application Laid-Open No. 07-31596 is known, which illuminates an eye fundus blood vessel with both a tracking laser beam and blood flow velocity measurement laser beam. This apparatus obtains the blood flow velocity in an eye fundus blood vessel and the vessel diameter of the measured blood vessel so as to measure the blood flow rate in the blood vessel.
The eye fundus blood flowmeter is an apparatus which illuminates an eye fundus blood vessel (to be examined) of an eye to be examined with a laser beam having a wavelength λ, receives the resultant scattered reflected light through a photodetector, detects an interference signal based on a Doppler-shifted component, which is scattered reflected light from a blood flow, and scattered reflected light from a blood vessel wall in a stationary state, and obtains a blood flow velocity by frequency-analyzing the signal. A blood flow velocity (maximum velocity Vmax) is obtained by the following principle.Vmax={λ/(n·α)}·||Δfmax1|−|Δfmax2||/cos βwhere Δfmax1 and Δfmax2 are the maximum frequency shifts calculated from the reception signals received by two light-receiving parts, λ is the wavelength of a laser beam, n is the refractive index of a measurement region, α is the angle defined by two light-receiving axes in the eye, and β is the angle defined by a plane formed by the two light-receiving axes in the eye and the velocity vector of a blood flow.
Such measurements in two directions cancel out the contribution of measurement light in the incidence direction. This makes it possible to measure a blood flow at an arbitrary region on the eye fundus. If the nodal line defined by the plane formed by two light-receiving axes and the eye fundus is matched with the velocity vector of a blood flow, then β=0°. As a consequence, a true maximum blood flow velocity can be measured.
This laser Doppler eye fundus blood flowmeter, however, requires a measurement time of a few seconds, and hence the ophthalmic technician must perform measurement while observing the state of an eye to be examined. In using such an apparatus that requires to simultaneously observe the state of data under measurement and the state of an eye to be examined, an observed image obtained by a TV camera is displayed on an observation monitor, and the state of data under measurement is displayed on the monitor of a personal computer for blood flow velocity analysis. The ophthalmic technician can simultaneously observe the state of data under measurement and the state of the eye to be examined by simultaneously observing the two monitors.
In the above prior art, however, two monitors, i.e., a monitor for observation of an eye to be examined during measurement and a monitor for displaying the state of data under measurement, must be separately installed, posing problems in terms of space and ease of observation. In addition, recently, with a video capture board or the like, video signals can be displayed on the monitor screen of a personal computer, and an observed image of an eye to be examined can be displayed on the monitor screen of the personal computer for blood flow velocity analysis, together with measurement results and measurement conditions.
However, many pieces of information, e.g., an observed image of an eye to be examined, the state of data under measurement, and measurement results, must be displayed on the monitor. Assume that measurement results and measurement conditions are preferentially displayed. In this case, in performing alignment for a blood vessel to be measured, an observed image of an eye to be examined becomes small and difficult to see. In contrast to this, if an observed image of an eye to be examined is preferentially displayed, measurement results become difficult to see.
A conventional apparatus which picks up an eye fundus image by a TV camera and allows an operator to position the apparatus, select a measurement region, and perform measurement while observing a TV monitor has been disclosed in Japanese Patent Application Laid-Open Nos. 07-136141 and 07-155299 and the like. However, the display zooming ration of such apparatuses can not be changed. An ophthalmologic apparatus capable of changing the display zooming ratio is disclosed in Japanese Patent Application Laid-Open No. 08-126611. These ophthalmologic apparatuses have the following drawbacks.
(1) In extracting a measurement position on the eye fundus of an eye to be examined and performing positioning to match the optical axis of the eye to be examined with the optical axis of an objective lens, a low display zooming ratio, i.e., allowing the operator to see a wide range on the eye fundus, is preferable in searching for a measurement position candidate on the eye fundus. When positioning is to be performed, a wide range on the eye fundus which can be seen allows the operator to check mixture of external disturbance light and the like and perform accurate positioning.
(2) In checking whether a blood vessel to be measured is accurately illuminated with measurement light, a higher display zooming ratio allows the operator to obtain more detailed information and hence to make accurate setting.
In method (1), however, since the display zooming ratio is constant, it is impossible to satisfy both the requirements. Although two display means may be prepared, a large space is required, and an increase in cost is inevitable.
In method (2), since a central position is fixed when the zooming ratio is changed, if an actual measurement position is not near the central position when the zooming ratio is increased, the measurement position falls out of the display range.
Furthermore, although the zooming ratio can be optically changed, a complicated arrangement is required to simultaneously change the central position and the zooming ratio, resulting in a large, expensive apparatus.